Influence of High-Pressure Steam Pretreatment on the Structure of Rice Husk and Enzymatic Saccharification in a Two-Step System

Abstract

This study aimed at developing an operational high-pressure steam pretreatment (HPSP) to effectively modify rice husk for enzymatic saccharification. The HPSP was performed at 160 to 200 °C under 0.3 to 2.8 MPa for 2 to 10 min. The efficiency of this method was based on the chemical composition, scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses. Optimum pretreatment conditions (200 °C, 1.85 MPa for 7 min), enzyme concentration at 30 FPU/g and temperature at 60 °C for 48 h of continuous saccharification effectively produced sugar (21.1 g/L = 0.422 g/g dry substrate) at a saccharification degree of 53.87%. Conducting a secondstep enzymatic saccharification resulted in additional sugar production (7.9 g/L = 0.158 g/g substrate) and a 20.44% saccharification degree. In contrast, the two-step saccharification process (48 and 24 h) achieved optimal sugar yield of 0.581 g/g substrate and saccharification degree of 73.5%. Additionally, the process improved the yield of monomeric sugars of glucose (0.465 g/g), xylose (0.010 g/g), and cellobiose (0.063 g/g). Therefore, the combination of the high-pressure steam pretreatment with thermostable cellulase from Bacillus licheniformis 2D55 in a two-step enzymatic saccharification process is an economically viable method in rice husk bioprocessing for sugar production.

Impact of pretreatment severity on fungal cellulase production on sugarcane bagasse substrate

“…There was a total loss of structure, with large openings on the fibres suggesting a loss of part of the cellulose content as indicated in the compositional analysis where the percentage composition of cellulose was lower than was recorded in the milder pretreatments. Similar disruption and loss of cellulose were previously reported by Kazeem et al [37] with high pressure steam pretreated rice husk at higher pretreatment conditions. Vera et al [5] showed that altered fibre characteristics of substrate can induce stress and affect fungal micromorphology, thereby impacting enzyme activity and efficiency.…”

Performance and mechanisms for V(v) bio-reduction by straw: key influencing factors

“… 28 The bands at 1000–1200 cm −1 indicated C–O–C stretching, C–O covalent bonds, and O–H bonds prevalent in cellulose, hemicellulose, and lignin. 29 The relative intensities significantly changed after V( v ) sorption, which indicated that the functional groups might be predominant functional groups for the removal of V( v ).…”

“… 36,37 Notably, at the end of the experiment, the fluorescence intensity of the humus-like area with a high initial V( v ) concentration (150 mg L −1 ) was higher than that of the humus-like area with low initial V( v ) concentration (10 mg L −1 ), which was consistent with the change rule of DOM reported in the cadmium contaminated soil with added wheat straw. 29 …”

Effect of steam explosion on the structural modification of rice straw for enhanced biodegradation and biogas production

“…The intensity of the peaks indicated that they were hemicellulose and cellulose (methyl and methylene). The intensity of the bands was reduced after the pressure increased (Kazeem et al 2017). The loss of aromatic units and changes in the lignin were identified by changes in the intensity of the band at 1649 cm -1 .…”

“…The increase in the intensity of this band might have been because of the dissolution of non-cellulose components, which caused an increase in the cellulose content in the rice straw (Ang et al 2012). The absorption band at 1430 cm -1 was related to amorphous cellulose (Kazeem et al 2017). The intensity of the band at 1430 cm -1 was reduced after the steam explosion pretreatment, which meant the amorphous part of the structure was degraded, especially after lignin structural changes occurred.…”